This invention relates to well apparatus, and more particularly to down hole oil tools that seal-in the liquid filled well bore.
During the development of an oil or gas well, various down hole tools are employed, some of which engage moveable sleeves within the well bore. The tools both seal to and lock onto the sleeve, and the sleeve is itself dynamically sealed to the well bore. The function of the tool is to move the sleeve downward.
Conventional practice is to drop a tool in the form of a blank dart down the well bore, where it engages the sleeve. Hydraulic pressure is then applied to the liquid above the dart to move it and the sleeve downward. If the column of liquid below the tool is large enough, the sleeve can be satisfactorily moved the required distance. However, if there is a plug closely below the landed dart, the volume of incompressible fluid in the resulting blind chamber establishes a pressure lock preventing the dart from shifting the sleeve or other down hole tool mechanism, thereby defeating the functional requirement of the system.